By Dr. Mercola
Blueberries are among my favorite foods, not only for their delicious taste, but also for their tremendous antioxidant and anti-inflammatory properties. Similar to other berries, blueberries are outstanding dietary sources of bioactive compounds, such as anthocyanins, ellagic acid, flavonols and resveratrol.
Blueberries are an excellent source of vitamins C and K, manganese and fiber. They are highly regarded for their role in helping reduce your risk of cancer, diabetes, heart disease and vision loss. Blueberries are a delicious treat particularly when plucked from a bush in your own backyard. While organic, store-bought varieties are expensive, you can easily plant a few bushes and harvest your own blueberries.
To ensure your blueberries will thrive, you'll need to invest some time ahead of planting to prepare your soil and select varieties well-suited for your climate. Given these extra steps, if you have blueberries in mind for a spring crop, you'll want to begin your preparations in the fall. Here's everything you need to know about growing blueberries.
Choose a Planting Location Where Your Blueberries Will Thrive
In the video above, David Handley, small fruit and vegetable expert with the University of Maine Cooperative Extension, explains how to choose a suitable location for your blueberry bushes. To thrive, your blueberries will need:
• Full sun: While blueberries can tolerate shade, you can maximize berry production by planting your bushes in an open area in full sun
• Soil drainage: Although blueberry bushes can tolerate very wet soil during periods of dormancy, be sure to choose a site with good drainage to ensure water runoff during the growing season; blueberries will not grow well in water-soaked soil
• Water source: Choose a location you can get water to easily and regularly; consider using a soaker hose or trickle-irrigation system
• Wind protection: If the offseason months are cold in your area, your blueberry bushes will benefit from a hedge for wind protection, which could be a building, fence or line of shrubs or trees.
If you are considering planting blueberries near an evergreen hedge, avoid (or plant at least 1,200 feet away from) balsam firs because they can exchange a disease called witches' broom1 with blueberries. Since this disease is nearly impossible to eradicate apart from using a toxic herbicide, which I discourage, prevention is your best strategy.
Prepare Your Soil Well Ahead of Time for Optimal Blueberry Growth
Because blueberries demand soil conditions quite different from traditional garden plants, you will need to take action well ahead of time to ensure optimal growing conditions. For your blueberries to thrive, garden experts suggest you will need soil that is:2,3
- Acidic: A soil pH around or slightly below 5.0 is recommended
- Compost rich: The best planting environment for blueberries is a 1-to-1 mix of soil from the planting bed (only after you've properly acidified it) and compost or peat moss
- Loose: Blueberries will thrive in sandy or sandy loam, but will suffer in compacted soil, such as clay
- Well-drained: As mentioned above, blueberries need well-drained soil to thrive, so choose a location with good water runoff and avoid swampy areas
If your current situation falls short in one or more areas, do not despair. For starters, review these soil restoration techniques. Specific to blueberries, there are steps you can take to create the necessary conditions.4 The key is to start well ahead of time. For example, if you want to plant blueberry bushes in the spring, you must begin preparing your soil the previous fall.
The most important first step is to complete a soil test. Contact your local cooperative extension office or order a test kit off the internet. You need to know if your existing soil can support blueberries, especially given their need for very acidic conditions.
If the area where you want to plant blueberries is currently covered by grass, you will most definitely need to lower the pH. Most lawns have a pH of 6.0 to 7.0. Before you can alter the pH, you will need to kill off the grass first. This can be accomplished by covering it with heavy plastic or a tarp for several months.
After the grass is dead, you can add sulfur, a natural mineral, according to the needs of your soil. The amount of sulfur to use depends on the results of the soil test, and will range from about 1 to 7 pounds per hundred square feet. It's best to indicate on your soil test paperwork your intention to plant blueberries (versus a generic reference to fruit trees or a garden).
When blueberries are indicated, the testing service should be able to tell you the proper amount of sulfur to use. You can buy sulfur from your local garden store or nursery in pellets or powdered form. Mix it into the top 6 inches of soil across the entire planting area.
Choosing Suitable Varieties for Your Climate
Once you've determined your soil will support blueberries, or made changes to ensure this, you can move on to select a suitable variety for your climate.5,6,7 Keep in mind you'll want to plant more than one type of blueberry bush due to the need these plants have for cross-pollination. Blueberry bushes will produce bigger fruit, and more of it, when planted with at least one other variety.
Another reason for planting more than one bush is the flexibility it will give you to extend your harvest. By planting multiple varieties with varying maturity dates, you will ensure a steady supply of berries throughout the entire growing season. No matter where you live, there is a type of blueberry best suited to your region. All four varieties need a period of prolonged cold to set their flowers. Given their unique constitution, some types need less time and coolness than others. The four major varieties include:
- Highbush (Vaccinium corymbosum): These large, dark blueberries typically found at your local market are so named because their bushes grow to be about 6 to 8 feet tall. Highbush plants come in either northern — for U.S. Department of Agriculture Plant Hardiness zones 4 to 7 — or southern varieties, for zones 7 to 10. Because the southern type has a low chilling requirement, highbush can even be grown in my home state of Florida.
- Lowbush (Vaccinium angustifolium): This type is super hardy and ideal for zones 3 to 6, especially in places where winter temperatures plummet below zero. As you might expect from the name, lowbush varieties are ground-hugging, diminutive bushes that grow just 6 to 18 inches tall. These bushes produce small, sweet berries. Most lowbush plants sold in nurseries are wild seedlings, meaning the plant size and fruit characteristics like appearance and taste will vary widely.
- Half-high: This variety originated from the desire growers had to produce a large berry consistent with Highbush with the cold tolerance of Lowbush. Half-high bushes grow 3 to 4 feet tall and produce a medium-sized berry. These bushes do well in containers and require less pruning than other types.
- Rabbiteye (Vaccinium virgatum or Vaccinium ashei): This heat- and humidity-tolerant type is suitable for zones 7 to 9, which gives southern gardeners a second planting option. Rabbiteye berries ripen later in the season and are smaller than high-bush berries. The bushes can grow upward of 10 feet tall. If you live in a mild climate and are concerned about your soil conditions, you'll be happy to know Rabbiteye bushes are less particular about their soil than the other types.
How to Plant Blueberries in the Ground
Once you've prepared your soil and selected the best blueberry variety for your area, you are ready to start planting. The best time for planting blueberries is early spring, during the six weeks prior to the last expected frost in your area. Whether you are planting bare-root or young container-grown plants, keep in mind they will need time to grow roots before the hot weather comes. Handley, as demonstrated in the video above, as well as other gardening experts offer the following tips as you begin the planting process:8,9
- Set your plants about 5 to 6 feet apart
- If you are planting a large number of bushes at once, maintain row spacing of about 8 feet
- Dig a hole large enough to allow you to set each bush slightly lower in the ground than they stood in their nursery row or pot; some recommend a hole about 2 feet deep and 6 feet wide
- After excavating the hole, you'll want to mix in a 1-to-1 ratio of compost or wet peat moss to the ground soil prior to placing it around the bush
- Break up the root ball and lightly separate the roots prior to placing each bush into its hole
- Fill in around the plant with your soil blend, packing it down firmly around each plant; leave a slight depression around each plant so it can collect and retain water
- Give each plant a thorough watering; after the water soaks in, water generously a second time
- Layer on about 3 inches of organic mulch, such as pine needles, sawdust, shredded leaves, straw or woodchips to keep the roots cool, aid in moisture retention and inhibit weed growth; never use sawdust from chemically treated wood
- Cut back to ground level all but the two most vigorous upright shoots
Because blueberry bushes will need 1 to 2 inches of water a week during the growing season, you may want to install a drip irrigation system or soaker hose to help you keep up with watering, particularly during dry periods. If you have hard water, which is alkaline, you may want to add 2 teaspoons of vinegar per gallon of water to maintain the acidic soil conditions blueberries need to thrive.
Growing Blueberries in Containers
Even if you have lots of outdoor space, you may decide to grow your blueberries in containers. For starters, controlling the acidity of the soil is a lot easier in a pot or container than in your garden or yard. Here's what you need to know to be successful with container-grown blueberries:10
- Use a large pot: Because blueberry plants can produce for several years, start with a pot at least 18 inches deep. Because you will be planting more than one plant for cross-pollination, you will need at least two to three large pots.
- Choose a potting soil designed for acid-loving plants: The quickest way to obtaining the soil your blueberries will need to thrive is to take a trip to your local garden store or nursery. There you can buy a potting mix designed for acid-loving plants such as azaleas or rhododendrons, which are in the same family as blueberries. You can also make your own blend at home by following the same instructions given earlier for in-ground plantings.
- Protect them in winter: If you live in a cold area, overwinter your blueberry containers in a protected area — against a building or fence — to shield them from the wind. Other options are to mulch your plants with straw or wrap them in burlap. While dormant plants don't need much moisture, water your blueberries a few times during the winter to ensure they do not completely dry out.
In addition to the items above, be sure to adhere to the instructions for in-ground plants related to the need for multiple bushes, full sun exposure, regular watering and annual fertilizing. All the same needs apply to both in-ground and container-grown blueberries.
Tips on Pruning Your Blueberry Bushes
As with most plants, pruning is a vital part of the growing process and required to maintain healthy blueberry bushes. If your bushes are not producing new stems annually and you have little growth to prune, step up your fertilization efforts and recheck your soil pH. Below are some suggestions on how to best accomplish pruning for blueberries:11,12,13
- For the first three years, generally speaking, blueberries will not need to be pruned
- During the first year or two, rub off the fruit buds to enable the bush to mature and become well established prior to fruit bearing
- In later years, prune your bushes annually in late winter to get rid of any old wood — this will help stimulate the growth of young, fruitful branches
- Prune any crowded, diseased or unproductive stems annually
- Make your pruning cuts close to the ground, and cut at an angle to encourage water runoff and disease prevention
After pruning, the buds that remain should develop larger, sweeter berries. The best time to prune is at the end of the growing cycle, when plants have lost their leaves but before new flower buds begin to open. You can give new life to lowbush varieties by cutting the plants completely to the ground every second or third year. Keep in mind lowbush will not produce fruit in the season immediately after pruning. This is yet another reason to plant more than one bush!
To ensure you will receive some fruit during lowbush pruning years, you may want to prune one-third or one-half of your bushes every second or third year. The stems for highbush blueberries produce for about six years. In the sixth year, you will want to prune these bushes to remove all stems either to the ground or with only the low, vigorous side shoots remaining. This is also a good time to thin out any crowded or diseased stems.
For Rabbiteye blueberries, cut the stems back by one-half the first year. To improve the health of 2-to-3-year-old bushes, remove any broken, crossing, diseased or spindly growth. When the plants are 4-to-5-years old, prune them annually to remove three to four of the oldest and largest woody canes. Pruning strategically near the center of the plant will improve light penetration and encourage new growth.
Check out the video below for a demonstration by the late Chuck Marsh on how to prune Rabbiteyes. Marsh was the founder and co-owner of the Useful Plants Nursery in North Carolina, a permaculture-based nursery specializing in healthy food and medicine plants.
Protecting Blueberries From Their No. 1 Pest: Birds
Fortunately, blueberries have few pests other than birds.14 Birds love berries, and will begin harvesting yours even when they are unripe. You can protect your fruit from winged poachers by covering your bushes with a light netting a few weeks before the berries ripen. Just be sure to secure the netting around the base of the tree to prevent entry. Because the plants need sun, do not cover them with any material that would block light.
Other defensive options to scare off birds include crop cages, fake owls or other fake predators, flash tape, pie pans, music and scarecrows.15 Find a deterrent that works best for you, or simply plan to share some (or all) of your harvest with the birds.
Harvesting and Preserving Your Blueberries
Store your unwashed blueberries in storage containers in the refrigerator, where they will keep for a week or more. Wash them before eating. You can freeze washed blueberries by spreading them out on a baking sheet and placing it into the freezer for a couple of hours. When the berries are individually frozen, place them in plastic bags and return them to the freezer where they will last throughout the winter season. Here's everything you need to know about harvesting blueberries:16
- Blueberries reach their full flavor and aroma a few days after they turn blue
- Pick blueberries at least twice a week when they ripen
- Berries that fall off in your hand with a slight movement of the branches are the truly ripe ones
- Blueberries eaten immediately after picking are at their nutritional peak
Because the nutritional value diminishes with freezing, grow multiple varieties to extend your growing season so you can eat at least 1 cup a day fresh from the bush. If you are looking for ways to use blueberries, there are many recipes online for canning blueberries and making low-sugar preserves and other treats.
Health Benefits of Blueberries
Blueberries are an excellent source of vitamins C, B6 and K, manganese and fiber. A 1-cup serving provides the following for your recommended dietary allowance:17
- Vitamin K: 36 percent
- Vitamin C: 24 percent
- Vitamin B6: 5 percent
- Manganese: 25 percent
- Fiber (3.6 grams): 14 percent
Blueberries also contain a decent amount of vitamins B1 (thiamin), B2 (riboflavin) and E, as well as calcium, magnesium, phosphorus and potassium. In addition to their vitamin and mineral content, the phytonutrients in blueberries provide important health benefits.
Blueberries pack tremendous antioxidant power, which helps your body keep free radicals in check and fight inflammation. (The Atlantic has published a fascinating article about how a blend of scientific research and marketing has led us to associate blueberries as being super healthy due to their high antioxidant content.18)
Along with other berries such as cranberries, raspberries and strawberries, blueberries are among the best dietary sources of bioactive compounds, such as anthocyanins, flavonols, ellagic acid and resveratrol. Studies indicate blueberries reduce your risk of:19,20,21
- Cancer: Blueberries have been shown to be effective in the fight against breast cancer, colon cancer, esophageal cancer and cancers of the small intestine, most likely due to their antioxidant and anti-inflammatory properties
- Eye problems: The antioxidants in blueberries are also known to help prevent or delay age-related eye problems and vision loss, including cataracts, dryness, infections, macular degeneration and myopia
- Excessive aging: Due to their high antioxidant content, blueberries can help reduce the signs of aging such as age spots, hair loss and wrinkles
- High blood sugar: Results from three prospective longitudinal cohort studies,22 involving more than 187,000 participants, concluded that greater consumption of specific whole fruits, such as blueberries, is significantly associated with a lower risk of Type 2 diabetes
- Urinary tract infections: Blueberries and cranberries contain an antioxidant called epicatechin that inhibits the growth of bacteria in the lining of your bladder that causes urinary tract infections
Blueberries Protect Your Heart
Blueberries are highly regarded for their role in helping protect your heart and lower your blood pressure. Past research revealed that women ages 25 to 42 who ate more than three servings per week of blueberries (and strawberries) had a 32 percent lower risk of having a heart attack.23 The primary agents responsible for protecting your heart are certain flavonoids found in the berries known as anthocyanins, antioxidants responsible for giving berries their colorful hues.
Anthocyanins are known to benefit the endothelial lining of your circulatory system, possibly preventing plaque buildup in your arteries, as well as promoting healthy blood pressure. Other research has shown these antioxidants to protect against heart disease by reducing oxidative stress and inflammation, while enhancing capillary strength and inhibiting platelet formation.24
Eating blueberries has also been shown to lower your blood pressure. A study published in the Journal of the Academy of Nutrition and Dietetics25 involving postmenopausal women suggests blueberry consumption positively affects blood pressure.
The women, who had either prehypertension or hypertension, received a placebo powder or freeze-dried blueberry powder — an amount equivalent to about 1 cup of fresh blueberries — daily for eight weeks. While the placebo group saw no significant changes, the women supplementing with blueberries realized a 5 to 6 percent drop in both their systolic (top number) and diastolic (bottom number) blood pressure readings.
Measurements of nitric oxide were also significantly increased in the blueberry group, with no such change in the control group. Nitric oxide helps your blood vessels maintain their elasticity and also dilates your blood vessels, thereby reducing your blood pressure. The study authors stated: "Daily blueberry consumption may reduce blood pressure and arterial stiffness, which may be due, in part, to increased nitric oxide production."
Blueberries Are Beneficial, but Don't Overdo It
While there's no doubt blueberries are a healthy food, you will still want to moderate your intake of them. One cup of blueberries contains approximately 15 grams of sugar. I continue to advise that you keep your total fructose consumption below 25 grams per day, including fructose from fruits such as blueberries. If you have a chronic disease such as diabetes, heart disease, high blood pressure or insulin resistance you'd be wise to restrict your fructose to 15 grams or less per day until your condition improves.
Please take note that blueberries are on the Environmental Working Group's list of 48 fruits and vegetables containing pesticide residue.26 Because both domestic and imported blueberries sold within the U.S. are sprayed with toxic pesticides, be sure to buy organic, or better yet, grow your own.